1. Field of the Invention
This invention relates to electrical connectors and, more particularly, to high density electrical connectors utilized to electrically connect electronic devices disposed on two or more printed circuit boards.
2. Description of the Prior Art
Increased integration of electronic devices has created an interconnection problem for printed circuit boards receiving these devices. Specifically, the number of interconnections required to electrically connect together two or more printed circuit boards receiving these electronic devices has exceeded the connection densities of prior art pin-in-socket connectors. Moreover, these prior art pin-in-socket connectors typically have relatively long and unshielded lengths which have uncontrolled impedances resulting in less than desired electrical performance.
A high contact density connector utilizable for electrically connecting together electronic devices received on two or more printed circuit boards and overcoming the foregoing problems is disclosed in an article entitled xe2x80x9cA High Density Edge Connectorxe2x80x9d by J. Campbell et al., Copyright 1995 IEEE. This article discloses a flex circuit formed of a 2 mil thick polyamide film having 3 mil wide copper lines plated onto one side thereof and 25 mil round contact pads plated on the side of the film opposite the circuit lines and along both edges of the film. 4 mil diameter plated through-holes, or vias, extend between the contact pads on one side of the film and the circuit lines on the other side. Palladium dendrites, or spires, are electro-deposited on surfaces of each contact pad. These dendrites straddle dust or fibers and puncture oils or films present on each contact pad prior to connector mating and produce on each contact pad a multitude of conductive connections. The connector includes a molded plastic force block to which elastomeric cylinders are molded. These cylinders act as springs which provide force, when compressed during assembly, to make and maintain an electrical connection between the contact pads on the film and the pads on a printed circuit board. One cylinder is provided for each contact and compensates for any variation in planarity and tolerance accumulation. Conical alignment pins are utilized to mate alignment holes in the flex circuit with alignment holes in the printed circuit board during assembly, thereby ensuring proper registration between the contact pads on the film and the pads on the printed circuit board.
Another flexible circuit connector for connecting a daughter card and a mother board is disclosed in an article entitled xe2x80x9cA High Density Pad-On-Pad Connector Utilizing A Flexible Circuitxe2x80x9d by R. S. Pokrzywa, Copyright 1993 IEEE. This connector utilizes a two-sided flex circuit having plated, spherical contacts contacting flat printed circuit pads on the daughter card and on the mother board. The spherical contacts on the flex circuit are 5 mils in diameter and have a copper base metal overplated with nickel and gold. Alignment pins are utilized to align the flex circuit, the daughter card and the mother board so that each spherical contact mates with a desired printed circuit pad. Precipitation hardened stainless steel curved beams provide contact force for reliable connection between the spherical contacts and the printed circuit pads. During actuation, the curved beam is flattened to produce a uniform load across the contact area. An elastomeric pad is positioned between the beam and the contact area to accommodate local discrepancies in load across the contact area and to focus the connector forces. In one embodiment, the elastomeric pad has a plurality of elastomeric cylinders utilized to back-up the spherical contacts. In another embodiment, where size does not permit molding individual cylinders for each spherical contact, an elastomeric rib is utilized to back a row of spherical contacts.
A problem with spherical contact pads and electro-deposited dendrites on contact pads is that they inconsistently break through contaminants, such as oxides, films or foreign materials, that may be present thereon or on the contact pad of a printed circuit board. Hence, inadequate electrical contact or, in some instances, no electrical contact is made between the contact pad of the flexible circuit and the contact pad of the printed circuit board. Moreover, the formation of a geometric surface such as dendrites or spheres on the contacts of the flexible circuit increases the cost of such connectors.
Currently available flexible circuits are expensive to manufacture and must be designed for specific applications. What is desired is a flexible electrical connector device that includes a compression means, yet is adaptable to different applications and is inexpensive to manufacture.
It is therefore an object the present invention to provide a flexible circuit compressor connector system that includes a compression assembly device which overcomes these drawbacks of the prior art connectors. It is a further object of the present invention to provide a flexible circuit compression connector system contact that promotes electrical contact with conductive pads of a printed circuit board tailored to specific applications. It is an object of the present invention to provide a method for making a flexible circuit compression connector system that utilizes a resilient compression assembly device to provide the required contact. It is an object of the present invention to provide a method of making a flexible circuit compression connector system that includes a resilient compression assembly that is less costly to manufacture than the prior art flex circuit connectors and is easy to assemble and align.
Accordingly, we have invented a flexible circuit compression connector system that includes a compression assembly utilized to electrically connect together conductive pads disposed on one or more substrates. The flexible circuit compression connector system includes a flexible insulating substrate having a plurality of predetermined positions of preapplied conductive material and at least one conductive line thereon extending between at least two of the predetermined positions of preapplied conductive material, such as a solder paste. The system also includes a plurality of contacts of preselected configuration forming a matrix which are assembled to the substrate. Each contact has a head and a base secured to the flexible insulating substrate at the predetermined positions of conductive material, thereby forming a contact matrix. The base and head are conductive materials. Each contact in the matrix has a head of preselected configuration extending away from the base and the flexible substrate. Each contact is conductive so as to allow a flow of current through the preapplied conductive material on the substrate and the base through the preselected configuration of the contact. In one configuration, the flexible circuit compression connector system includes a flexible substrate having a plurality of conductive holes therein and at least one conductive line thereon extending between at least two of the conductive holes. The flexible circuit compression connector system also includes a plurality of contacts. Each contact includes a base and a head that extends away from the base. Optionally the base may include a post that extends away from the base in a direction opposite the head. The base or the optional post of each contact is secured in one of the plurality of conductive holes.
A compression mat is positioned on the side of the flexible substrate opposite the heads of the plurality of contacts. The compression mat includes a plurality of resilient cylinders extending away from a resilient base. Each resilient cylinder has a distal end alignable with each one of the plurality of contacts, but on the side of the flexible substrate opposite the contact heads.
In assembling the contacts to the flexible substrate, a transfer film is utilized to transfer the plurality of contacts to the flexible substrate. The disposable transfer film preferably has a plurality of elastically deformable receiving apertures which receive and secure the head portion of preselected configuration of the plurality of contacts.
A flexible cable assembly is attached to a first substrate, such as a rigid printed circuit board, which has a plurality of the conductive pads on a surface thereof and at least one conductive line connected to at least one of the conductive pads. The rigid substrate and the flexible circuit compression connector system are alignable so that a portion of the head of each contact on one end of the flexible substrate is aligned in registration with one of the conductive pads on the surface of the rigid substrate.
A means for compressing the compression mat against the contacts is positionable adjacent the resilient base of the compression mat. The means for compressing urges together at least a portion of the head of each contact on one end of the flexible cable to the conductive pad of the printed circuit board or assembly in registration therewith. The resilient columns of the compression mat contact the side of the flexible substrate opposite the heads of the contact matrix of the flexible substrate so that each resilient column is aligned opposite a contact of the contact matrix. The resilient columns act as springs when compressed and urge the contact heads on the contact matrix of the flexible substrate against the conductive pads on the surface of the mating assembly, typically the rigid substrate such as a printed circuit board. In an alternative configuration, each resilient column of the compression mat contacts the distal end of an optional post of a contact, the post extending through the flexible substrate and functions as the spring when compressed to make and maintain good electrical connection between the contact head and corresponding conductive pad.
Preferably, a plurality of alignment holes in each of the flexible substrate, the rigid substrate and a surface that includes the compression mat co-act with plurality of alignment members to align the flexible substrate, the rigid substrate and the compression mat so that the resilient cylinders are in registration with the contacts, and the heads of the plurality of contacts are in registration with the plurality of conductive pads. Each alignment member may be threaded and may serve the dual purpose of producing the compressive force for compressing the mat against the flexible substrate opposite the heads.
The present invention is a flexible circuit compression connector system comprised of at least one contact that includes a conductive head and a conductive base. The conductive head extends from one side of the base and is of a preselected design most suitable for its intended application. An optional post may extend from the side of the base opposite the head.
The base of the contact is secured to the flexible substrate at predetermined positions with a conductive material such as solder while a preformed head of preselected configuration extends away from the base. In an alternative configuration, the side of the base opposite the post can have a cavity formed therein in registration with a lengthwise axis of the post. The base can have a periphery having a generally rectangular outline. Each comer of the generally rectangular outline of the base can be rounded and can include one of the plurality of projections. Each projection can have a rounded edge formed continuous with the periphery of the base.
The present invention includes a method of making a flexible circuit compression connector system that includes a compression assembly having a connector that includes providing a plurality of contacts forming a matrix, each contact having at least a base and a head of preselected configuration selected on the basis of its intended application, the head projecting away from the base. The contacts are preformed by a metal working operation into any suitable preselected head geometry, the contacts being connected together by ribs. The heads of the plurality of contacts are inserted into a plurality of receiving apertures in a thin transfer film which captures the contacts so that the heads project through one side of the transfer film while a portion of the contacts are projected from the opposite side of the film. Thin ribs connecting the contacts are then separated from the contacts. A flexible insulating substrate is provided with preapplied conductive material applied at a plurality of predetermined positions. At least one conductive line extends between and electrically connects at least two of the predetermined positions of preapplied conductive material. The transfer film containing the contacts and the flexible substrate are mated by bringing the side of the transfer film having the portion of the contacts projecting from the transfer film opposite the heads into registry with the preapplied conductive material on the flexible substrate. This portion may be bases or optional posts. By application of heat, the contacts are fused to the preapplied conductive material on the flexible substrate. The transfer film is then separated from the flexible substrate so that the heads of the contacts project away from the surface of one side of the flexible substrate.
In the alternative configuration, a method of making the flexible circuit compression connector system that included a connector that includes providing a plurality of contacts, each contact having a base with a post and a head. The heads of the plurality of contacts are inserted into a plurality of receiving apertures in a disposable transfer film so that a portion of the post connected to the base opposite the head extends out of the plurality of receiving apertures. A flexible substrate is provided having a plurality of through-holes therein and a plurality of conductive lines thereon. At least one conductive line extends between and electrically connects at least two of the through-holes into which the conductive bases are inserted. The through-holes preferably are conductive. The transfer film and the flexible substrate are mated so that at least a portion of each base of the plurality of contacts are received in the plurality of conductive through-holes in the flexible substrate. The portion of the bases, which may be the aforementioned posts, of the plurality of contacts are fused to the plurality of through-holes in the flexible substrate. The transfer film is then separated from the flexible substrate and the plurality of contacts.
The plurality of contacts are formed from a strip of conductive material by any conventional metal forming method. Each contact is connected to an adjacent contact by a rib formed from the conductive material strip during the metal forming operation. Each contact is excised from its connecting rib after insertion into one of the receiving apertures in the transfer film. Each receiving aperture elastically deforms to receive and retain the contact therein.
An advantage of the present invention is that it provides a flexible cable including a compression assembly which overcomes the drawbacks of the prior art connectors. The present invention provides a flexible circuit compression connector system having a compression assembly that includes an electrical connector that utilizes the compression assembly to promote positive contact between the connector and the conductive pads of a mating circuit. The present invention also provides an improved method for making a flexible circuit compression connector system that utilizes the provided compression assembly to assure positive contact with a mating assembly. The present invention also provides a method of making a flexible electrical cable and connector that is easier, more reliable, more readily adaptable to modifications, including field modifications, and less costly to manufacture than the prior art flex circuit connectors.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.